Hybrid vehicles may have many different powertrain configurations. In one configuration, two torque producers may provide torque to the transmission. An electric machine may be used to provide torque and charge a battery and a combustion engine may also be used to provide torque. The electric machine and engine may be selectively connected or separated by a disconnect clutch to provide torque to the transmission either jointly or separately.
When shifting to a higher gear, the torque provided to the step ratio transmission is normally reduced to counter inertia torque. This event is referred to as torque reduction during transmission upshift, or upshift torque reduction. If torque is not reduced during an upshift of the transmission, a noticeable torque spike will be felt by vehicle occupants. In vehicles having an internal combustion engine, torque is normally reduced by retarding the spark. In diesel engines torque is reduced by reducing the quantity of fuel supplied to the engine. A step ratio transmission may be provided for a hybrid vehicle with the above configuration. However, because torque is provided from two sources to the transmission, conventional approaches to reducing torque by reducing only the engine torque are ineffective because torque may be provided by the electric machine.
This disclosure is directed to solving the above problem and other problems relating to controlling a hybrid vehicle powertrain to reduce torque during upshift operations of a step ratio transmission.